1. Technical Field
Various embodiments of the present invention relate to an electronic device. More specifically, the exemplary embodiments of the present invention relate to a semiconductor memory device.
2. Related Art
Semiconductor memory devices are memory devices implemented using a semiconductor such as silicon (Si), germanium (Ge), gallium arsenide (GaAs), or indium phosphide (InP). Semiconductor memory devices are generally classified into volatile memory devices and nonvolatile memory devices.
A volatile memory device is a memory device that loses stored data when a power supply is cut off. Examples of a volatile memory device include a static random-access memory (SRAM), a dynamic RAM (DRAM), and a synchronous DRAM (SDRAM). A nonvolatile memory device is a memory device that maintains stored data even when the power supply is cut off. Examples of a nonvolatile memory device include a read-only memory (ROM), a programmable ROM (PROM), an erasable programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a flash memory, a phase-change RAM (PRAM), a magnetic RAM (MRAM), a resistive RAM (RRAM), and a ferroelectric RAM (FRAM). The flash memory is largely classified into a NOR type and a NAND type.
Some of memory cells of a semiconductor memory device are defined as flag cells. Flag cells store data for managing main cells. As the degree of integration of memory cells increases, the risk of damaging data stored in flag cells may increase. For example, as a distance between memory cells decreases, various factors, such as a threshold voltage difference between memory cells and a high driving voltage, may increase the risk of damaging the data stored in memory.